The present invention is directed to minimally invasive surgical systems and methods of use thereof. More specifically, the present invention is directed to computerized systems for operation of atherectomy instruments and methods for intravascular surgery to increase blood flow in a lumen of a blood vessel. The disclosures of U.S. Pat. Nos. 5,350,390, 5,806,404 and 5,697,459, issued to Sher, are incorporated herein by reference in their entirety.
Atherosclerosis is the principal cause of heart attacks, stroke, gangrene and loss of function of extremities. It accounts for approximately 50% of all mortalities in the USA, Europe and Japan. Atherosclerosis is characterized by a build-up of fatty deposits in the intimal layer of a patient's blood vessels. Very often over time, what is initially deposited as relatively soft cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, which results in chest pain or even in cases severe restriction, to heart attack. Restriction of blood flow, which leads to heart attack, is also explained by another mechanism known as vulnerable plaque. It happens to people that do not have severely narrowed arteries. In fact the vulnerable plaque may be buried inside the artery wall and may not always bulge out and block the blood flow through the artery. Inflammation combined with other stress e.g., high blood pressure can cause the covering over the plaque to crack and bleed, spilling the contents of the vulnerable plaque into the blood stream. Blood cells that recruit to the site of injury can form a clot large enough to block the artery. It is of enormous importance that the physician will have the capability of imaging the lesion morphologically as well as the plaque composition. There are imaging techniques that perform these tasks. The modalities of imaging techniques will be detailed later.
The present therapeutic strategies for severe atherosclerosis in coronary arteries rely on angioplasty procedures (e.g., percutaneous trans-luminal coronary angioplasty (PTCA), atherectomy devices, stent implantation, excimer laser angioplasty, etc.), and coronary artery bypass surgery (CABG). Transluminal angioplasty refers to a technique of dilating significantly blocked arteries from inside, thus avoiding the need for much more extensive surgical intervention (CABG).
Conceptually, atherectomy devices have the advantage of positively removing the plaque. In the balloon (PTCA) and the stent procedures the plaque is not removed but rather pushed towards the blood vessel wall. Several kinds of atherectomy devices are currently available but their performances have not stood up to the expectations and will be discussed later. A major disadvantage of the stent is that it causes in-stent restenosis, a phenomenon that will be explained later. Stent implantation involves deployment of a foreign body that evokes a reaction of the immune system. The stent and the balloon have the advantage that the procedure is relatively simple and easy to use.
Today the stent is the common procedure for clearing blocked arteries (97% of more than 2 million procedures world wide). Atherectomy devices are used only for specific procedures such as debulking of calcified lesions where it is difficult to open the lesion with the balloon.
To date none of the available techniques provides a total safe and effective solution to blocked arteries. The problems that still exist in clearing blocked arteries are described below:
Restenosis—
Restenosis is re-occlusion of a peripheral or coronary artery following trauma to the artery caused by efforts to clear an occluded portion of the artery by angioplasty, such as, balloon dilation, stent implantation, atherectomy or laser ablation treatment. The rate of restenosis following treatment with these angioplasty procedures is about 30-50% depending upon the vessel location, lesion length and a number of other variables. Restenosis occurs also in grafts that are used to bypass blocked arteries. Restenosis results in significant morbidity and mortality and frequently necessitates further interventions, such as repeat angioplasty or coronary bypass surgery. Thus, there is a need for methods and devices for preventing and/or treating restenosis. Preferably, these methods and devices should be specific in their effect, easy to administer, and effective in the long run with minimal adverse side effects. The processes responsible for restenosis are not completely understood.
One aspect of restenosis may be simply mechanical, caused by the elastic rebound of the arterial wall. Another aspect of restenosis is believed to be a natural healing reaction to the injured arterial walls that were damaged by angioplasty procedures. The final result of the complex steps of the healing process which involve local inflammation is intimal hyperplasia, and migration and proliferation of medial smooth muscle cells, until the artery is again occluded.
The existing, FDA approved, atherectomy devices have shown a high rate of restenosis (30-50%). Atherectomy devices have also additional technical problems. The AtheroCath (Guidant) is complex to use, is pushed across the lesion and offers inconsistent results. It has a high rate of blood vessel perforation. The Rotablator (Boston Scientific) is applicable only to moderate to heavily calcified atherosclerotic plaque lesions. It does not cut the plaque but rather pulverizes it while rotating at a very high speed. This causes problem of heating the blood vessel and also to the phenomenon known as No Reflow in which blood does not flow in the vessel even though the lesion was opened.
In another type of atherectomy device, the cutting head does not rotate. An example of this type of device is U.S. Pat. No. 5,409,454 to Fischell. In this type of device, the cutting head is first pushed across the lesion and then pulled back. While pulled back the cutting head shaves the atheroma. Pushing the catheter across the lesion causes trauma to the blood vessel.
My U.S. Pat. No. 5,350,390 describes an atherectomy device, that addresses the trauma problem. However, my own earlier teachings do not include the idea that removal of a lesion may begin prior to transversal of the lesion by a guidewire. This serious inherent disadvantage is addressed by the teachings of the present invention, as will be detailed hereinbelow. In order to differentiate the claimed invention from those earlier teachings, the invention will be referred to hereinbelow as Apparatus for Removal of Intraluminal Occlusions (ARIO)
In-Stent Restenosis—
The mechanical aspects of restenosis have been successfully addressed by the use of stents to prevent elastic rebound of the vessel, thereby reducing the level of restenosis for many patients. The stent, though, has created a new problem called in-stent restenosis, namely the occurrence of excessive late intimal hyperplasia due to excessive cell proliferation that can restrict blood flow within the stent itself. In-stent restenosis occurs in 20-30% of stent procedures and in many cases CABG is required to solve the problem.
Brachytherapy and drug coated stents are approaches aimed to reduce in-stent restenosis. Brachyterapy provides only partial solution to in-stent restenosis. The drug coated stents succeeded in reducing in-stent restenosis from 20-30% to 5-9% but failed to eliminate it. The drug-coated stent is a new procedure. In follow-up tests, problems such as late incomplete apposition emerged, however no long-term results are currently available.
Existing atherectomy devices such as the Rotablator and AtheroCath were tested for clearing in-stent restenosis, but the results were disappointing. ARIO, due to its mild mode of operation is a suitable candidate for clearing in-stent restenosis.
Perforation—Coronary artery perforation is a rare but important complication of percutaneous revascularization. Perforation has been reported in lesions treated with PTCA and Stents and at much higher rate in atherectomy devices. During PTCA or stenting perforation may occur as a consequence of guidewire advancement, balloon inflation or balloon rupture. Regardless of the device, the risk of perforation is increased when complex lesion is present (chronic total occlusion, vessel bifurcation, severe tortuosity in artery). Clinically, coronary perforation is associated with a high incidence of death.
Total Occlusions (TO) is a formidable obstacle for physicians. Physicians cannot see the path for the guidewire through the TO because the flow of the angiography contrast media is stopped by the blockage. There is a higher risk of perforation or damaging the vessel than with normal angioplasty. U.S. Pat. No. 6,228,076 to Winston is an example of controlling the path of the guidewire across a lesion using OCT. Another example for TO crossing is U.S. Pat. No. 6,120,516 to Selmon.
Bifurcation: Percutaneous coronary intervention (PCI) in bifurcation lesions is challenging. It has lower procedural success and high rates of restenosis compared with non-bifurcation PCI.
A great part of the problems described above can be solved if the physician is provided with means for imaging the arteries. An important and standard imaging modality is angiography. However, angiography enables the physician to see only a general view of the arteries, where the details of the plaque are not clear. Several modalities that can give a detailed image of the plaque have been suggested. These modalities allow the physician to visualize the morphology as well as the composition of the plaque. Subsequently, the physician can position the working head of the intraluminal catheter at a desired location. This procedure could minimize remarkably the risk of blood vessel perforation.
The imaging modalities can be classified in the following hierarchical manner:
There are two types of blood vessel imaging techniques, non-invasive and minimally invasive. The non-invasive modalities include CT (X-ray Computer Tomography), MRI (Magnetic Resonance Imaging), ECBT (Electron Beam Computer Tomography), etc. In current non-invasive technology the resolution of the image is poor and therefore this type of imaging can be used for a general view of the arteries. The minimally invasive imaging can be divided into two classes: The first incorporates an imaging sensor into or on the catheter. This class is exemplified by U.S. Pat. No. 4,794,931 to Yock, which describes an atherectomy device with ultrasonic imaging capabilities.
The second class incorporates a sensor into a guidewire. The second class can be divided into two sub-classes. The first sub-class produces a cross sectional image of the lumen e.g., IVUS (Intravascular Ultrasound)—U.S. Pat. No. 6,459,921 to Belef, OCT (Optical Coherence Tomography)—U.S. Pat. No. 6,445,939 to Swanson, MRI (Magnetic Resonance Imaging)—U.S. Pat. No. 6,377,048 to Golan. This sub-class is relevant to the present invention, as the operation of the device is based on the fact that the physician can see a cross sectional view of the lumen.
The second sub-class does not provide a cross sectional image of the lumen. It provides other kind of information related to the lumen e.g., Thermography supplies thermal mapping of the interior of the lumen, U.S. Pat. No. 6,228,076 to Winston, describes a system which receives interferometric data from the tissue, etc.
Prior art describes a device that incorporates an imaging guidewire that can produce a cross sectional view of the lumen into an intravascular catheter. U.S. Pat. No. 5,938,609 to Pomeranz describes an imaging guidewire with an ultrasound sensor. The movable imaging guidewire includes a fixed guidewire tip attached to its distal end. The movable imaging guidewire is first positioned within the vascular system so that its fixed guidewire tip extends beyond the stenosed region, and than the intravascular catheter is inserted over the movable imaging guidewire. This mode of operation renders it suitable for balloons procedures. The disadvantages of this type of movable imaging guidewire are similar to the standard guidewire, i.e., the mechanical requirements of pushability and crossability are high. The operational disadvantage is high risk of perforating the blood vessel or in case the occlusion is too severe the guidewire cannot cross it.